Transistors, in particular metal oxide semiconductor field effect transistors (MOSFETs MOSFET=Metal Oxide Semiconductor Field Effect Transistor), enjoy numerous applications in all areas of electronics, from power electronics through to large scale integrated circuits, for example memory components.
With the increasing reduction of feature sizes in integrated components and the associated scaling of the field effect transistors, various problems have to be surmounted. These include in particular the diffusion of the source or drain region or of the dopants thereof into the channel region below the gate and the formation of space charge regions between the source and drain regions, on the one hand, and the channel region, on the other hand. Both effects reduce the effective length of the gate. In order that the effective length of the gate has a minimum value, the distance between the source region and the drain region must therefore have a minimum magnitude and cannot be decreased to the desired extent. This prevents or restricts further miniaturization.
A gradual improvement is conventionally achieved by means of so-called halo implantations at the pn junctions or by reducing the implantation dose. The halo implantation is complicated since it requires additional method steps. Reducing the implantation dose reduces the number of degrees of freedom in the design of the component and results in particular in a reduction of the charge carrier density and of the electrical conductivity.
Insofar as the shortening of the effective length of the gate is not prevented or compensated for, it results in an increase in the leakage current or a reduction of the source-drain resistance in the switched-off state of the field effect transistor. If the field effect transistor is the selection transistor of a memory cell of a memory circuit, the increased leakage current results in a faster discharge of the storage capacitor. This in turn requires an increase in the capacitance of the storage capacitor or a shortening of the refresh circles of the memory component. Both adversely affect the power demand and the thermal budget of the element.